JP2559789B2 - Method of detecting machining error in die-sinking electric discharge machining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention eliminates a series of machining errors such as errors due to machining gap changes and machining depth errors that occur during electrical discharge machining, and errors due to electrode wear and thermal deformation. It relates to a method of detecting.

[Conventional technology]

The die-sinking electric discharge machine is widely used in various industries centering on the die industry, and among them, NC controlled electric discharge machines capable of controlling multipurpose machining are becoming popular.

Generally, an NC controlled electric discharge machine is roughly divided into a machine body that performs electric discharge machining and a control power supply body with a built-in NC control device that performs a series of controls as shown in FIG. An X, Y table 4 having a built-in X-axis and Y-axis drive mechanism is mounted on the bed 3, and a processing tank 5 is arranged on the top of the bed so that the workpiece 2 of the product to be processed can be mounted therein. I'm running. The quill 6 having a built-in Z-axis electrode feed mechanism is supported by a column 7, and the electrode 1 is attached to the tip of the quill. 8 is a processing liquid supply device, and a processing tank 5
In order to supply and circulate the machining liquid inside, and to appropriately discharge machining products (machining scraps, decomposed products of machining fluid, etc.) generated by electric discharge machining, the vicinity of the electric discharge machining between the electrode 1 and the workpiece 2 Even so, an appropriate amount of working fluid can be supplied. On the other hand, the NC control device 9a built in the control power supply main body 9
Can set and register arbitrary processing conditions and control the processing power supply circuit 9c, and at the same time control the positioning of the electrode 1 and the workpiece 2 via the 3-axis drive control circuit 9b, and also the Z-axis electrode feed mechanism. Drive and control of the electrode position during machining, drive and swing control of the X-axis and Y-axis table mechanism, and a series of controls required for electrical discharge machining can be performed. Electric discharge machining has been conventionally performed using the die-sinking electric discharge machine configured as described above, but with the recent advancement of industry, there is a demand for high-efficiency machining as well as high-efficiency machining. It is high.

Most of the machining accuracy of a molded product by electrical discharge machining is determined by the finishing process, but there are many factors related to machining, so if you do not fully understand the characteristics and mutual relations of each factor, you can effectively improve the precision of machining. I can't. Factors related to machining accuracy are classified into (1) mechanical factors, (2) control factors, (3) electrical discharge phenomena factors, (4) temperature factors, and (5) other factors as shown in Table 1 below. Can be. Countermeasures against these factors include physically easy ones and difficult ones. In particular, regarding the item (3), the phenomenon peculiar to electric discharge machining is involved, so the countermeasures are difficult.

Among them, a machining error due to a machining gap change that occurs during electric discharge machining and a machining error due to electrode wear are pointed out as major factors that roughly impair high precision machining. Further, since the temperature of the machining liquid rises during the electric discharge machining, thermal deformation and thermal expansion error caused by this temperature change also become a major cause of rough damage. Further, the setting error caused by the positioning of the electrode and the workpiece before machining is one of the factors that cannot be overlooked. A situation in which such an error occurs will be specifically described here by taking hole drilling as an example.

FIG. 15 and Tables 2, 3, and 4 show an outline of the machining plan and condition selection for the machining specifications of the workpiece, and the calculation method of the electrode feed amount and swing radius according to this machining process. It is a thing. Table 2 is a hole drilling example, Table 3 is the drilling plan, and Table 4
Shows a method of calculating the electrode feed amount and the swing radius.

Further, FIG. 16 shows an example of a flow chart of a machining operation for actually carrying out machining using the die-sinking electric discharge machine shown in FIG. Generally, electrical discharge machining is performed in several steps from the first rough machining to the final finishing machining, and each machining condition includes machining speed, machining surface roughness, electrode wear rate, gap between electrodes (machining gap), etc. Select appropriate conditions from the processing technology data file that describes the characteristics. Needless to say, since the discharge energy is large under the conditions of rough machining, high-speed machining can be performed, and under the conditions of finish machining, the discharge energy is small and low-speed machining is performed in order to obtain the required machined surface roughness. Further, in order to suppress or eliminate the influence of electrode consumption, the condition that the electrode consumption rate is as small as possible is selected.

The electrode feed amount in the depth direction and the oscillating amount in the radial direction are generally obtained by adding or subtracting the machined surface roughness value and the gap gap value under each machining condition as shown in Table 4. It is set based on each. In the first machining, it is not necessary to perform the oscillation (r ₁ = 0), but if the electrode diameter to be used is smaller than the predetermined value, the oscillation amount is added to correspond to the predetermined value. Can be processed.

The machining contents planned in this way are programmed, input to the NC-controlled electric discharge machine, and electrodes and workpieces of a predetermined shape are set at predetermined positions. Then, after the preparation for the processing is completed, the actual processing operation is started, and the processing operation is executed like the flow chart shown in FIG. Step K indicates the order of processing steps, where K = 1 to 6
Becomes At this time, the target value Z _K of the electrode feed amount is Z _{1 to} Z ₆ , and the machining is sequentially repeated until the final finishing machining Z ₆ (Z _n ) is reached. FIG. 17 shows the state of the processed hole and the electrode feed amount at this time. The swing radius at the time of final processing is also shown in the figure. The reference plane in the depth direction can be set arbitrarily according to the object to be machined, but here it is the workpiece upper surface of the machined hole for easy understanding.

This reference plane setting before machining is conventionally performed by a method of sensing contact between an electrode and a workpiece, and the same method is used here. The electric discharge machining is performed in the depth direction from the reference surface, and the electrode position is controlled so as to keep the machining gap within a certain proper range by following the progress of the machining. As a method of controlling the machining gap, a method of detecting the average machining voltage between the electrodes and controlling the average to be constant has been simple and widely used conventionally. There are several other control methods, but in any case, unless the machining gap is kept within an appropriate range, the electric discharge phenomenon is disturbed and normal electric discharge machining cannot be maintained. It is also necessary to discharge the processed product from the machining gap so as not to adversely affect the electric discharge machining.

When processing is performed by such a method, the first error that occurs is a positioning error before processing. The alignment setting (reference plane setting) by contact sensing is easily affected by burrs that are easily formed at the end of the electrode and dust, dust and other inclusions adhering to the surface of the workpiece, and the error amount (ΔO _Z ) Is a few μ
Since it may range from m to several tens of μm, accurate reference plane finding is extremely difficult. As another alignment method other than the contact detection, there is a detection method utilizing corona discharge by applying a high voltage, as disclosed in Japanese Patent Publication No. 61-58255. If this detection method is used, it is possible to avoid the above problems, but a special high-voltage power supply and control device of about 1000 V, which is much higher than the normal electric discharge machining voltage, is required, and safety is high. Also be careful. Further, although it is possible to utilize the corona effect in air, it is difficult to handle it in the same way as in air because the phenomenon is different when used in liquid and during processing.

On the other hand, the machining gap during electric discharge machining is not always constant, but increases and decreases according to various machining conditions, and fluctuates up and down in accordance with a change in the electric discharge machining phenomenon due to the influence of a machining product. Therefore, the preset machining gap (GAP) value does not occur, and the amount of difference from this set value becomes the machining error. FIG. 18 and Table 5 show the state of the electrode position and the gap error after the step K processing when the method shown in FIG. 16 was used for processing. That is, if the actual gap value G _a with respect to the set value G _K is too large (G _K <G _a ), processing is excessive, and if it is very small (G _K > G _a ), processing is insufficient. I will end up. The amount of difference from the set value is greatly affected by electrical discharge and machining phenomena,
It may range from m to several tens of μm.

Furthermore, since the temperature of the working fluid rises during working, thermal expansion deformation occurs due to this temperature change. Further, even in the processing under the low wear condition, the electrodes are consumed during the processing. The situation at that time is shown in FIG. 19, FIG. 20, and FIG. In FIG. 19, the electrode 1 is installed on the tip of the quill 6a via the electrode fixing jig 6b, and the workpiece 2 is installed on the table 4a via the workpiece fixing jig 4b, and the machining liquid (Fig. (Not shown)
It is inside. V _w is a processing volume when the electrode 1 having a predetermined shape is processed to a predetermined depth, and V _c is a consumed volume at that time,
In addition, Δl _c is the electrode wear length assuming that the wear is uniform, and ΔL _e and ΔL _w are the thermal expansion deformation amounts on the electrode side and the workpiece side caused by the temperature rise of the working fluid, respectively. There is. On the other hand, the relationship between the processing time t until reaching the target processing depth H _K , the temperature change ΔT at that time, and the electrode wear length Δl _c is shown in FIGS. 20 and 21. When the discharge energy is large and the machining speed is fast v ₁ , the target machining depth is reached in a shorter time than when the machining speed is slow v ₂ , and the temperature change ΔT ₁ also becomes large. The electrode wear length increases in proportion to Δl _c , the electrode wear rate δ _K and the working depth, and Δl _c = A ・ H _K・ δ
_Indicated by _K. This value causes a negative error with respect to the processing dimension accuracy. On the other hand, the thermal expansion causes the deformation ΔL to increase in proportion to the temperature change, and ΔL = (L _e · ρ _e + L _w ·
ρ _w ) ΔT, which is a positive error factor with respect to the machining dimension accuracy. Fig. 22 and Table 6 summarize the results shown in Fig. 20 and Fig. 21, and if the electrode wear is excessive (Δl _c > ΔL), the processing becomes insufficient, and conversely, due to temperature change. If the thermal deformation is excessive (Δl _c <ΔL), excessive machining will result. The temperature change depends on the processing conditions,
Under rough machining with a large discharge energy, the temperature may reach 10 ° C. or higher, and the thermal deformation caused by this can reach several tens of μm, often exceeding the electrode consumption value.

As described above, (1) alignment error occurring before machining, (2) error due to electrode wear occurring during machining, (3) error due to thermal expansion deformation due to temperature change (4) error due to machining gap change, etc. are related to each other. As shown in Table 6, the processing dimensional accuracy will be affected.

Therefore, it is necessary to solve each of these error factors in order to improve the precision of processing, and a method of detecting the effectiveness for that purpose has been strongly desired. Although several detection, detection methods and correction control methods have been proposed so far,
At present, there is no suggestion of what can accurately detect and eliminate the above errors.

As a device for controlling the temperature of the working fluid, for example, Japanese Patent Laid-Open No. 61
As disclosed in Japanese Unexamined Patent Publication No. 86130, there is a device that preheats a working fluid by a preheating device and at the same time circulates it through the main body of the working machine to keep a constant temperature during working. By using such a device, the problem of error due to temperature change can be avoided, but other error factors cannot be solved at once. For this reason, another method must be used,
In addition, since the above device is a large-scale device, it is functional,
There are financial problems.

On the other hand, as a method of detecting electrode wear, for example, as disclosed in Japanese Patent Laid-Open No. 55-150937, the electrodes are opposed to the electrode tip detection plate before and after electric discharge machining and weakly discharged to detect the tip position. There is a method of detecting the electrode consumption based on the change. It is considered to be a promising means for detecting electrode wear, but since the electrode tip detection plate is fixed at a position that is considerably distant from the workpiece to be machined, there is a possibility that it may interfere with the alignment with the workpiece. . Although the weak discharge is supposed to be performed for a short time, the state of the gap at that time is not disclosed at all. Since the surface condition of the electrode tip before and after machining is different, the gap condition at the time of weak discharge should have changed, and if the influence is not taken into account, the position of the electrode cannot be accurately detected, which causes an error. May increase. The thermal deformation due to the temperature change is not disclosed at all.

In addition, as a method of measuring and correcting the processing error,
For example, as disclosed in Japanese Patent Laid-Open No. 58-160018, there is a method of interrupting the processing midway, measuring the processing depth using a measuring probe, and then correcting the error from the desired depth. However, since there is a processed product at the bottom of the processed hole immediately after the processing, it is likely to be affected by the processed product, and it is considered that accurate measurement is difficult. Therefore, a work for removing the processed product or a special removing device is required, and the above-mentioned method requires a large measuring device, which is problematic in terms of function and economy.

[Problems to be Solved by the Invention]

The present invention has been made in view of the above-mentioned technical problems and problems of the prior art, and utilizes the characteristic that the gap in a gap detection condition of a certain minute discharge converges to a specific value, and Accurately set the alignment with the workpiece, and
Detects errors caused by machining gap changes that occur during electrical discharge machining,
Another object of the present invention is to provide an effective method for detecting an error due to electrode wear and thermal deformation and a series of processing errors in the processing depth direction.

[Means for solving the problem]

According to the present invention, the electrode after the gap is converged while the minute discharge is generated for a predetermined time while switching to the gap detection condition in which the gap with the electrode has a specific value during or after the step designated in the machining process. It is characterized in that the position is detected, and an error due to a change in the working gap or an error in the working depth caused at the time of working is detected from the detection result. Also,
According to the present invention, before the start of machining, a micro discharge is generated under a gap detection condition in which a gap with an electrode has a specific value at a specific position on a reference plane setting table installed at a predetermined position or a work surface that can be substituted for it. After generating for a predetermined time and setting the reference plane in the machining depth direction by detecting the position, start the predetermined machining, and then after moving the specified step, move the electrode to the position of the reference plane setting. At the same time, the gap detection conditions are switched to, a minute discharge is generated for a predetermined time to detect the electrode position after the gap is converged, and it is generated at the time of machining from the comparison result of the detected value and the value set before the start of machining. A processing error due to electrode wear and thermal deformation was detected. In addition, after detecting a machining error due to the above-mentioned electrode consumption and thermal deformation,
The electrode position is detected after the electrode is moved to the machining hole again and the gap is converged while the minute discharge is generated for the predetermined time under the gap detection condition. It is characterized in that each of the machining depth and the machining error in the machining depth direction is detected. Further, in the present invention, after a series of processing from roughing to finishing is completed, the electrode is moved to the position of the reference plane setting and the gap detection condition is switched, and the machining depth direction is changed by the same method as before the start of machining. After resetting the reference plane, the error due to electrode consumption and thermal deformation is corrected by this resetting, the electrode is transferred to the processed hole again, and a minute discharge is generated for the predetermined time under the gap detection condition. However, it is characterized in that the electrode position after the gap is converged is detected, and the processing error with respect to the processing depth and its target value is detected from the detection result.

The detection method according to the second claim of the present application uses a die-sinking electric discharge machine to feed an electrode from a predetermined position to a workpiece in a predetermined depth direction, and a series of machining from rough machining to finish machining. In the method of detecting the machining error that occurs during machining of the workpiece while controlling the electrode feed to the step value, a reference plane setting table installed at a predetermined position or the upper surface of the workpiece that can be used as a substitute before machining is started. At a specific position, a minute discharge is generated for a certain period of time under the condition that the gap between the electrode and the electrode has a specific value, and after the position is detected, the reference surface in the machining depth direction is set and then the predetermined machining is started. And then,
After machining the step specified in the machining process, the electrode is moved to the position of the reference plane setting and switched to the gap detection condition, and the electrode position is detected after the minute discharge is generated for a predetermined time to converge the gap. It is characterized in that a machining error due to electrode wear and thermal deformation occurring during machining is detected based on a comparison result between the detected value and a value set before the machining is started.

The detection method according to the first claim of the present application uses a die-sinking electric discharge machine to feed an electrode from a predetermined position to a workpiece in a predetermined depth direction, and to perform a series of machining from rough machining to finish machining. In the method of detecting a machining error that occurs during machining of a workpiece while controlling the electrode feed in the order of steps, before starting the machining, the reference plane setting table installed at a predetermined position or the workpiece upper surface that can be substituted At a specific position, a minute discharge is generated for a predetermined time under the gap detection condition where the gap with the electrode becomes a specific value, and after setting the reference surface in the machining depth direction from that position detection, the predetermined machining is started. After that, after the step specified in the processing step is performed, the electrode is moved to the position for setting the reference surface and switched to the gap detection condition, and the electrode position after the minute discharge is generated for a predetermined time to converge the gap. Inspect Then, after detecting the machining error due to electrode wear and thermal deformation that occurred during machining from the comparison result of the detected value and the value set before machining start, move the electrode again to the machined hole and Detects the electrode position after converging the gap while generating a minute discharge for a predetermined time, and detects the machining error due to the machining gap change and the machining depth and the machining error in the depth direction that occurred during machining from the detection result. It is characterized by doing so.

The detection method according to the second claim of the present application uses a die-sinking electric discharge machine to feed an electrode from a predetermined position to a workpiece in a predetermined depth direction, and a series of machining from rough machining to finish machining. In the method of detecting a machining error that occurs during machining of a workpiece while controlling the electrode feed in the order of steps, before starting the machining, the reference plane setting table installed at a predetermined position or the workpiece upper surface that can be substituted At a specific position, a minute discharge is generated for a specified time under the condition that the gap between the electrode and the electrode has a specified value, and after the position is detected, the reference surface in the machining depth direction is set and then the specified machining is started. After finishing a series of machining from the rough machining to the finishing machining, the electrode is moved to the position of the reference plane setting and the gap detection condition is switched, and the machining depth direction is changed by the same method as before the machining is started. Re-establishment of reference plane After correcting the error due to electrode consumption and thermal deformation by this resetting, the electrode was transferred to the hole after processing again, and the gap was converged while the minute discharge was generated for the predetermined time under the gap detection condition. The feature is that the rear electrode position is detected, and the processing error with respect to the processing depth and its target value is detected from the detection result.

[Action]

As described above, in the present invention, the position setting (reference plane setting) between the electrode and the workpiece before processing is performed by performing minute discharge for a predetermined time under the gap detection condition where the gap has a specific value. Therefore, it is possible to accurately set the reference plane, and it is possible to eliminate the alignment error that is likely to occur in the conventional contact sensing method. Further, in the present invention, the processing error due to the change in the processing gap that occurs during processing is diagnosed by utilizing the characteristic that the gap in the gap detection condition converges to a specific value. In addition, it is possible to detect accurately, and it becomes possible to easily perform the correction control, which was difficult to be dealt with by the conventional technology. In addition, since the error due to electrode consumption and the error due to thermal deformation that occur during processing are diagnosed by the same method as above, it is possible to accurately detect the subtraction error amount of both and easy subsequent correction control. Is possible. Furthermore, in the present invention, after the machining is finished, the electrode is reciprocally moved to the set position of the reference surface and the bottom position of the machining hole, and a minute discharge is performed for a predetermined time under the gap detection condition, and the detection result of the electrode position at that time is obtained. Since the machining depth and its machining error are diagnosed more, the machining gap error, the electrode wear error, and
A comprehensive processing error in the processing depth direction such as a thermal expansion deformation error can be detected quickly and accurately. Based on these diagnostic results, the correction control of the machining error can be easily performed, and the precision of the electric discharge machining can be improved.

〔Example〕

Hereinafter, the content of the present invention will be specifically described with reference to Examples. FIG. 1 is an example of a flow chart of a machining operation showing the contents of the present invention. The reference plane is set before machining according to the gap detection condition, and the error caused by electrode wear and thermal deformation occurring during machining is detected and corrected. Further, a method for detecting a series of processing errors in the processing depth direction including an error due to gap deformation is disclosed.
Further, FIGS. 2 to 4 respectively explain the contents disclosed in FIG. In the present invention, since the reference plane in the depth direction is set before machining, as shown in FIGS. 2 and 3, the reference plane setting base 27 installed at a predetermined position first determines the gap. A minute discharge is generated for a predetermined time under the gap detection condition that has a value. As the installation place of the reference surface setting table 27, an appropriate place is selected according to the shape of the object to be processed, and if possible, a place close to the processed hole is preferable. The following Table 8 shows processing conditions.

Further, if the reference plane setting table can be substituted, the reference plane can be set even on the upper surface of the workpiece. In this figure, the height H _c of the reference surface setting table may be set to 0. The gap detection condition here is a condition in which the discharge energy is extremely small as in the case of performing the best surface machining, and the applied voltage may be the same level as the normal machining condition. Predetermined time (eg 20-60
The gap with the electrode 1 becomes constant (g _c ) by the minute discharge. It stops at the point where the gap is constant, and the point where g _c is subtracted from the electrode position Z _d0 at that time is the upper surface of the reference surface setting base 27, which is the reference surface (Z ₀₀ = Z _d0 + g _c = 0). The amount processed by the minute discharge is negligible and can be ignored. Further, the gap value g _c is stable with a small fluctuation range of ± 2 μm or less. After accurately setting the reference plane in this way, the electrode is moved to the processing position to start the predetermined processing. The predetermined machining is the same as in the past (see FIG. 16), but in the present invention, as shown in FIG. 1, the machining error in the depth direction is diagnosed after the machining of the designated step. The diagnostic method is performed according to the procedure shown in FIGS. 4 to 6 and the following Table 9.

The electrode feed amount at the specified machining step has reached the target value (Z _a = Z _K ), and the machining is completed.
After moving to the reference surface setting table 27, the gap is converged while shifting to the gap detection condition and causing intermittent minute discharge due to the vertical movement of the electrode for a predetermined time. Electrode position after the convergence
Z _d0 ', as shown in FIG. 5, changes by the difference between the electrode consumption error .DELTA.l and temperature changes due to thermal deformation error ΔL generated during machining, Z _d0' becomes = (Δl _c -ΔL) -g _c . Therefore,
The amount of error due to electrode wear and thermal deformation can be detected from changes in the electrode position before and after machining (ΔZ _d0 = Z _d0 ′ −Z _d0 ) (ΔZ _d0 = Δl _c −ΔL). Further, the above error can be corrected by resetting the reference plane here. That is, by resetting Z _d0 ′ = Z _d0 = −g _c , the error is corrected as shown in FIG. 6 and Table 9 (Δl _c −ΔL = Δ
Z _Ll ). Then, the electrode after the resetting of the reference plane is moved again to the machining hole position and sent in the depth direction, and then the gap detection condition is re-established, and intermittent micro-discharge due to vertical movement of the electrode is generated for a predetermined time. Converge the gap. Electrode stop position at the point where the gap converges and becomes constant (g _c ).
Z _da ′ becomes Z _da + ΔZ _Ll . ΔZ _Ll is further related to the amount of error due to electrode wear and thermal deformation corrected in the previous stage. Based on the correlation between the electrode position immediately after machining (Z _a = Z _K ), and the electrode position after micro-discharge due to the gap detection condition where the gap converges to a specific value as described above, the machining gap G _a during machining And the gap error amount ΔG for the set value G _K are calculated as shown in Table 9 (Δ
G = G _K −G _a = G _K − (Z _da −Z _a + g _c )). Similarly, the machining depth H _a during machining is Z _da + ΔZ _Ll + g _c
Is calculated as _{-H c = Z a + G a} + ΔZ Ll -H c, further objectives of the machining process to the depth H _K depth error _{(ΔH K = H K -H a} )
Can be calculated and ΔH _K = ΔG + ΔZ _Ll = ΔG + Δ
It becomes 1−ΔL. When the value of ΔH _K is positive (H _K > H _a ), it means that the working depth is insufficient and the gap during working is too small or the electrode wear is too large. On the contrary ΔH _K
If the value of is negative (H _K <H _a ), the gap is too large or the thermal deformation is larger than the electrode wear. If it is determined that the correction processing is necessary based on this result, the error amount may be corrected to ΔH _K = ΔZ _K and the processing may be restarted.
Since the processing error detection timing and number of times can be specified arbitrarily,
It may be carried out after finishing the intermediate step as well as after finishing the final step.

As described above, according to the present invention, a series of machining errors in the machining depth direction, such as errors due to electrode consumption and thermal deformation that occur during machining and errors due to gap changes, can be detected and diagnosed quickly and accurately. It becomes possible to perform correction control of a processing error, which is difficult to deal with by the technology, and by using the present invention, it is possible to significantly improve the processing accuracy.

7 and 8 show another embodiment of the present invention, which shows a method of detecting and correcting an error due to electrode wear and thermal deformation. For the reference plane setting based on the gap detection condition performed before the start of machining, the reference plane setting base was used in the above-mentioned FIG. 2, but here it is not used and a small electric discharge is directly generated on the upper surface of the workpiece near the machining position. The example disclosed is disclosed. The procedure for detecting a predetermined machining operation and an error due to electrode wear and thermal deformation that occur during machining is the same as that described above, but the following error correction processing is configured here to be performed in the next step. There is. As shown in Fig. 7, after the electrode feed amount in the specified step machining reaches the target value (Z _a = Z _K ) and the machining is finished, the electrode is moved to the same reference plane position as when machining is started. As it moves, it switches to the gap detection condition where the gap becomes a specific value. Then, as shown in FIG. 8, by causing an intermittent minute discharge due to the vertical movement of the electrodes for a predetermined time,
It is possible to avoid the effects of irregularities on the electrode surface and deposits that occur during processing, and the gap between the electrode and the workpiece surface converges to a specific value (g _c ). The stop position Z _d0 ′ of the electrode after convergence changes by a difference between the electrode wear error Δl _c and the thermal deformation error ΔL from the time before machining (Z _d0 = −g _c ), and Z _d0 ′ = (Δl _c − ΔL) -g _c . From this result, it is possible to detect the amount of error (ΔZ _d0 = Δl _c −ΔL) due to electrode wear and thermal deformation that occurred during processing.

Table 10 summarizes various conditions of the example in FIGS. 8 and 9.

Further, by resetting the electrode position with respect to the reference plane (Z ₀₀ = Z _d0 + g _c = 0) as Z _d0 ′ = Z _d0 = −g _c , error correction (Δl−ΔL = ΔZ _Ll ) can be easily performed. The error correction processing is executed in the next step processing. The timing and the number of times of the above-mentioned error detection can be arbitrarily designated according to the machining shape and size of the workpiece, machining conditions and the number of machining steps. As shown in the machining plan shown in FIG. 16 and the like, in a machining example in which the number of steps from the first rough machining to the final finishing machining is 6 times (machining steps K = 1 to 6, n = 6), If the timing of error detection in FIG. 7 is designated as, for example, K = 1 and K = n-1, error detection is executed twice after the first rough machining and after the final machining. Further, the error correction after the error detection is performed by the processing of K = 2 and K = n = 6, which are the next steps, respectively. In the final finishing process, since the processing volume is small, the errors due to consumption and thermal deformation are minimal, and there is almost no effect. By doing so, it is possible to quickly eliminate the thermal deformation error and the electrode wear error due to the temperature change that is most likely to occur in the rough machining process in which the discharge energy is large and the machining volume is large. Further, it is possible to eliminate the error thereafter, and it is possible to improve the processing accuracy without fear that the processing depth after processing is excessively large. In addition,
Here, an example in which the error detection is executed twice has been shown, but it goes without saying that the number of times may be further increased, and the first detection time may be designated and changed to another step.

FIG. 10, FIG. 11, FIG. 12, and Table 11 show another embodiment of the present invention and show a method of detecting and correcting a processing error due to a gap change occurring in a predetermined processing process. In the course process the specified step, first, to determine the start timing as shown in FIG. 11, for example, the electrode position Z _a value at a point where the electrode feed amount Z _a in the processing reaches the Z _K-beta calculate. After that, the gap is a specific value g _c
Then, the gap is converged while the intermittent minute discharge due to the vertical movement of the electrode is generated for a predetermined time, and the electrode position after the convergence is calculated in the same manner as above.
Since the electrode position fluctuates every moment according to the change of the discharge phenomenon, a stable measurement position (for example, a point at the timing time t ₁ ) is determined, and the value at that position may be measured several times and averaged. . It takes some time for the gap to converge to a specific value because the machining products from the previous stage remain, and it is necessary to exhaust it sufficiently. It has a role to promote. The convergence time t _c is about 30 to 60 seconds. If the above arithmetic processing is to be simplified, it may be determined from the electrode stop position after the required machining and the minute discharge are finished as described in FIG.

The gap value G _a during processing than measured both variation Δg _c = Z _d -Z _a electrode position calculating _{G a = Δg d + g c} ) and, at the same time, the depth in the machining H _a is also calculated (H _a = Z _d + g _c ). Then, next, the gap error amount ΔG _K with respect to the gap value G _K during the machining plan can be calculated (ΔG _K = G _K −G _a ), and the machining depth error ΔH _GK can also be calculated at the same time (ΔH _GK = H _K −β−H _a = ΔG _K ). From this result, the error amount is corrected to the electrode feed amount (ΔZ _GK = ΔG _K
= ΔH _GK ) and restart the machining. Electrode feed amount after correction
Z _K ′ becomes Z _K + ΔZ _GK .

By doing so, it is possible to easily detect and eliminate an error due to a gap change or a processing depth error that occurs during processing. The above-mentioned error detection can be designated to be performed not only in the final step machining step as shown in FIG. 10 but also in the intermediate step machining step. Further, here, the start time of error detection is set to the point of Z _a = Z _K −β (during processing), but it can be set to Z _a = Z _K (after processing), and the calculation processing of the electrode position can be performed. It will be simple.

 Table 11 below shows the operating conditions shown in Figs.

Finally, FIG. 13 shows the overall structure of a die-sinking electric discharge machine for carrying out the present invention. In the figure, a machining power source 9 connected to the electrode 1 and the workpiece 2 outputs a pulse voltage and a current corresponding to predetermined machining conditions and gap detection conditions instructed by the NC control device 11. The inter-electrode voltage detection circuit 24 detects the inter-electrode voltage of the discharge generated between the electrode 1 and the workpiece 2, and outputs the detection signal to the NC control device 11 and the electrode feed servo control circuit 16.
To determine whether the discharge state is good or bad. Electrode 1 is Z
Electrode feed mechanism 12 connected to the axis pulse servomotor 13
It is installed at the tip of the and is driven and controlled by the electrode feed servo control circuit 16 through the amplifier 15. The electrode feed servo control circuit 16 operates in response to a command signal from the NC control device 11 and appropriately controls the electrode position in accordance with the result of discrimination of the discharge state under each machining condition. In addition to this, it also has a function of periodically moving the electrode 1 up and down under specified processing conditions and gap detection conditions. Pulse servo motor 13
The pulse encoder 14 connected to detects the moving position of the electrode 1 with respect to the position command, and the detection signal is fed back to the electrode feed servo control circuit 16 and the NC control device 11.

The workpiece 2 set on the X, Y table 4 is mounted on the X, Y table mechanism 17, and the X, Y table drive control circuit 23.
Controlled by. A series of control commands for aligning the electrode 1 and the workpiece 2 and for swinging the workpiece 2 are transmitted from the NC controller 11. The pulse motors 18 and 19 for driving and the pulse encoders 20 and 21 for movement detection have the same functions as the Z axis. The machining fluid is supplied and circulated (not shown) from the machining fluid supply device 8 to the machining tank 5, and at the same time, an appropriate amount of the machining fluid is also supplied to the vicinity of the electric discharge machining, and the machining product can be appropriately discharged from the machining gap. It is becoming like this.

On the other hand, the error detection circuit 25 detects a change in the electrode position before and after the transition to the gap detection condition in which the gap converges to a specific value, and based on the detection result, an error due to electrode wear and thermal deformation that occurs during machining, and the machining It detects and diagnoses a series of machining errors such as errors due to gap changes and machining depth errors.It operates according to the command signal of the NC controller 11 and the signal from the electrode feed servo control circuit 16 and also detects and diagnoses it. The result is transmitted to the NC control device 11 and the error correction control circuit 26. Further, the error correction control circuit 26 sets an error correction corresponding to the error detection and the diagnosis result, and at the same time, sends a control signal for instructing the electrode feed correction and the correction processing to the NC control device 11.

By using the die-sinking electric discharge machine configured as described above, the detection, diagnosis, and correction control of the machining error in the above-described electric discharge machining of the present invention are executed, and the object can be achieved.

The present invention described above is not limited to the round hole shape shown in the embodiment, but can be applied to a wide variety of shapes and a plurality of rows of shapes. Further, instead of the Z axis feed, the X axis or The present invention can be applied to the case where a lateral hole or a lateral groove is processed while the Y-axis is feed controlled, if the control in the axial direction is changed.

〔The invention's effect〕

As described above, the present invention utilizes the characteristic that the gap converges to a specific value under the gap detection condition during a certain minute discharge,
Set the alignment before machining, detect and diagnose errors due to gap changes and machining depth errors that occur during electric discharge machining, detect errors in electrode wear and thermal deformation, and correct them. Since it is also possible to detect and diagnose the processing error of, it is possible to set the accurate reference plane, eliminate the error that is likely to occur in the conventional contact sensing method, and at the same time, correct the error correction that was difficult to cope with with the conventional technology. It becomes possible to control, and by using the present invention, the working accuracy can be greatly improved. Further, since the detection method of the present invention can be performed quickly and accurately with a simple circuit, it is possible to omit the measurement of a processing error after interrupting the processing and the labor thereof, and to use a special measuring instrument. It is not necessary and has a functional and economic effect.

[Brief description of drawings]

FIG. 1 is a flow chart of a machining operation showing an embodiment of the machining error detection / correction of the present invention, and FIGS. 2, 4, 5, 6 and 8 are examples of FIG. 1 respectively. FIG. 3 is a second diagram showing the positional relationship showing the movement of the electrode to be used and the workpiece in each process.
FIG. 7 is a diagram showing the relationship between the electrode operation and time for explaining the movement of the drawing, FIG.
The figure is a characteristic diagram showing the change with time of the electrode operation in the example of FIG.
10 and 11 are flow charts of the machining operation showing still another embodiment of the present invention, FIG. 12 is a characteristic diagram showing the time-dependent change of the machining result according to the flow of FIG. 11, and FIG. A layout diagram showing the overall configuration of the die-sinking EDM machine to be implemented, FIG. 14 is a perspective view of a conventional die-sinking EDM machine, and FIG. 15 is a dimension definition explanatory diagram that defines machining conditions in a hole machining example, 16 is a flow chart of the machining operation according to the conventional example, FIG. 17 is an enlarged view of the vicinity of the machining hole showing the relationship between the machining hole and the electrode feed amount, and FIG.
FIG. 19 is an explanatory view of the electrode position and the situation of occurrence of a gap error when processed by the conventional method, FIG. 19 is a sectional view showing the positional relationship of the processing apparatus similarly by the conventional method, and FIG. 20 is the conventional example of FIG. FIG. 21 is a characteristic diagram showing an error occurrence situation caused by electrode wear, and FIG. 21 is a characteristic diagram showing an error occurrence situation caused by thermal deformation.
FIG. 22 is an explanatory diagram of the electrode wear and thermal deformation occurrence state when processed by the conventional method of FIG. 1 ... Electrode, 2 ... Workpiece, 27 ... Reference leveling stand, 28 ...
... machining holes.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Ishii 2100 Kamiimaizumi, Ebina, Kanagawa Pref. Hitachi Seiko Co., Ltd. Yasushi Nakamura (56) Reference JP-A 58-160018 (JP, A) JP A 61-279429 (JP, A) JP 58-114821 (JP, A) JP 55-131440 (JP, A)

Claims (2)

(57) [Claims] 1. A die-sinking electric discharge machine is used to feed an electrode from a predetermined position to a workpiece in a predetermined depth direction, and
In a method of detecting a machining error that occurs during machining of a workpiece while controlling the electrode feed in a series of machining steps from rough machining to finishing machining, a reference plane setting table installed at a predetermined position before machining starts or At a specific position on the upper surface of the work that can be substituted for it, a minute discharge was generated for a predetermined time under the gap detection condition that the gap with the electrode became a specific value, and the reference plane was set in the machining depth direction from that position detection. After that, a predetermined machining is started, and after the machining of the step specified in the machining process, the electrode is moved to the position of the reference plane setting and the gap detection condition is switched to generate a minute discharge for a predetermined time. The electrode position after the gap is converged is detected, and after comparing the detected value with the value set before processing, the electrode wear and the processing error caused by thermal deformation that occur during processing are detected. The electrode position is detected after the electrode is moved to the machining hole again and the gap is converged while the minute discharge is generated for the predetermined time under the gap detection condition. A method of detecting a machining error in die-sinking electric discharge machining, characterized in that the machining error in the machining depth and the machining error in the depth direction are respectively detected. 2. A die-sinking electric discharge machine is used to feed an electrode from a predetermined position to a workpiece in a predetermined depth direction, and
In a method of detecting a machining error that occurs during machining of a workpiece while controlling the electrode feed in a series of machining steps from rough machining to finishing machining, a reference plane setting table installed at a predetermined position before machining starts or At a specific position on the upper surface of the work that can be substituted for it, a minute discharge was generated for a predetermined time under the gap detection condition that the gap with the electrode became a specific value, and the reference plane was set in the machining depth direction from that position detection. After that, after starting a predetermined machining and finishing a series of machining from the rough machining to the finishing machining, the electrode is moved to the position of the reference plane setting and the gap detection condition is switched to before the machining is started. By resetting the reference plane in the machining depth direction by the same method as described in (1) and correcting the error due to electrode consumption and thermal deformation by this resetting, the electrode is moved again to the hole after machining and the gap detection line In die-cutting electric discharge machining, which is characterized by detecting the electrode position after converging the gap while generating a minute electric discharge for a predetermined time and detecting the machining depth and its target value from the detection result. Method of detecting machining error.